Western Antarctica warming confirmed

Dec. 23, 2012
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Map of Antarctica showing the extent of surface melting in January 2005 observed from space. Byrd Station is located approximately 700 miles from the South Pole. (Bottom) Time series of mean January temperature at Byrd Station from 1957 to 2011 with the warm January 2005 highlighted with a yellow circle. / Google Earth; G. Picard (LGGE)

by Dan Vergano, USA TODAY

by Dan Vergano, USA TODAY

Western Antarctica has warmed unexpectedly fast over the last five decades, weather records confirm, adding to sea-level rise concerns in a warming world.

Temperatures in West Antarctica have increased at a rate nearly twiceas large as the global average, a 4.3 degree Fahrenheit increase since 1958, conclude meteorologists in the journal, Nature Geoscience, out Sunday.The finding adds Western Antarctica to the list of hot spots most affected by global warming, the century-long increase in global average temperatures largely driven by greenhouse gas emissions from burning oil, gas and coal.

"The magnitude of the increase is substantial," says polar meteorologist David Bromwich of Ohio State University, who led the study. "One of the most surprising aspects of this warming (increase) is how much is going on in the summer, that's the time we would get any melting." Bromwich had expected increases in rates of warming to be fairly uniform across the seasons, instead.

Antarctica's Byrd Station temperature records reconstructed by the researchers find that year-by-year temperature increases accelerated there mostly in the 1980s. While melting of the West Antarctic Ice Sheet now contributes only a few millimeters of sea level rise per decade (comparable to Greenland), the collapse of the 10 million square-mile Western Antarctic Ice Sheet underneath the station would trigger a 10-foot rise in sea level over a few centuries. The ice sheet rests frozen in a basin at sea level, and the fear is that it could slide into ocean waters if melting occurs at its base, raising water levels like an ice cube dropped into a glass.

"The rapid warming in West Antarctica is not a cause of ice sheet melting-- but it is a symptom," of warmer ocean waters reaching Antarctica that actually do much of the melting, says climate scientist Eric Steig of the University of Washington in Seattle. Publication of the new temperature record study, "marks a definitive end to a significant controversy," Steig says, started when his own team first published snow records in 2009 that surprised climate scientists by finding larger-than-expected temperature increases in Western Antarctica.

"I think this is news only in fitting into a pattern of studies showing warming in this (Western Antarctic) region," says polar expert Ted Scambos of the National Snow and Ice Data Center at the University of Colorado, Boulder. "Temperatures are still largely below freezing in Western Antarctica, unlike Greenland, even with the warming seen in the study."

Isolated by ocean waters from other continents, Antarctica offers a number of puzzles to climate scientists, largely due to its remoteness, which precludes collection of extensive weather records. Separate from ice sheets resting on land, sea ice surrounding Antarctica waxes and wanes with the seasons, reaching a maximum 7.5 million square miles in extent this year in October, according to NASA.

One of the paradoxes of climate change is that Antarctica's sea ice extant has grown in recent decades, as more powerful northward winds from the continent refreeze sea ice during the southern hemisphere's winter. The winds are stronger in part due to global warming adding more energy to polar weather systems. But overall, the entire continent has seen warming increase in line with the global average over the last few decades.

"A very large amount of water is locked up on land in Antarctica, and if the ice sheet shrinks, the ocean rises," says Penn State climate scientist Richard Alley, by e-mail. In Western Antarctica, "The new study does not give us new estimates of just when, or even if, we should be worried about these prospects for large parts of West Antarctica, but the new study points in useful directions for helping to answer those questions."